1. Field of the Invention
The present invention relates to a knock detection apparatus for detecting a knock generated in an internal combustion engine and for controlling an ignition timing.
2. Description of the Related Art
It is generally known that ion is generated if fuel is burnt within a cylinder of an internal combustion engine. Therefore, if a probe to which a high tension voltage is applied is provided within the cylinder, it is possible to observe this ion in terms of the ionic current. Also, if the knock is generated in the internal combustion engine, since a vibratory component of the knock is superimposed on the ionic current, it is possible to detect the generation of the knock by extracting this vibratory component therefrom.
FIG. 10 is a circuit diagram showing a conventional knock detection apparatus using the ionic current. First of all, in this circuit, an ignition plug 1 is used as a detection probe for the ionic current. A high tension voltage (bias voltage) for detecting the ionic current by utilizing a secondary voltage of an ignition coil 2 is charged to a bias means 3. When the discharge for the ignition has been completed, the bias voltage charged during the discharge period is applied to an end of the plug 1 to detect the ionic current.
In this apparatus, a knock detection circuit 4 shapes a vibratory component, extracted from the ionic current, into a pulse form on the basis of a predetermined threshold value. A change of the number of pulses of the pulse form is calculated by an ECU 5. The ignition timing is adjusted by the result and the generation of the knock is suppressed.
In general, a peak value of the ionic current is changed in accordance with a kind of fuel or an operational condition of he internal combustion engine. However, there is a tendency that at a low rpm, the ionic current is small and at a higher rpm, is larger. The value thereof is in the range of several xcexcA to several hundreds of xcexcA.
FIG. 11 is a block diagram showing the knock detection circuit 3 shown in FIG. 10 in more detail. When the ionic current is fed by the high tension voltage applied by the bias means 3, the ionic current is distributed into a mask 9 and a BPF (band pass filter) 8 for extracting the vibratory component by a current distributing means 7. The mask 9 is composed of a means for shaping the form of the ionic current by the predetermined threshold value to generate a pulse and a means for masking the pulse for a predetermined period of time for interrupting the noise by the ignition. The combustion/misfire may be judged in accordance with the pulse which will be referred to as a combustion pulse.
A window 10 starts an integration (charge) of the ionic current when the combustion pulse is turned on. When this integrated value reaches a predetermined value, a knock detection window is opened. The output is fixed by output limit 14 so as not to generate the knock pulse until the integrated value reaches the predetermined value. Also, when the combustion pulse is turned off, the knock detection window is closed.
After the vibratory component of the knock has been extracted by the BPF 8, it is amplified by an amplifier 11. The vibratory component is shaped in accordance with the predetermined threshold value in a comparator portion 13 so that the knock pulse is generated. The predetermined threshold value is set in a knock detection threshold setting portion.
FIG. 12 shows an operative shape example of each section of the circuit shown in FIG. 11. Also, FIG. 13 is an S/N graph of the number of the knock pulses upon the knock/non-knock.
The knock pulse detected as mentioned before is transmitted to the ECU 5. In the ECU 5, a background level (knock judgement level) is calculated from the number of the knock pulses under the regular operational condition (when the knock is not generated). Then, it is judged that the knock is generated when the knock pulse exceeding the background level is generated, so that the ignition timing is changed in response to the knock strength in a direction in which the knock is not generated. When the knock is not generated, the ignition timing is likely to be gradually returned to the predetermined value to thereby perform the knock control.
However, if additives (such as K or Na) are mixed into the fuel, the ionic current is increased to a magnitude that is several time larger than that of the usual case even if the amount of the additives are small like several ppms. The ionic current has the same original frequency component. When the ionic current is increased, this frequency component becomes the same as the vibratory component upon the knock generation. In spite of the non-knock condition, the number of pulses is increased, so that the S/N ratio of the knock/non-knock disappears. There is a problem that the knock control is impossible. FIG. 14 shows the S/N ratio upon the containment of the additives measured under the same operational condition of the internal combustion engine as in that shown in FIG. 13.
The element relating to the increase/decrease of the ionic current is a time change of the internal combustion engine or the shape of the ignition plug in addition to the fuel characteristics described above. In these cases, the same problem might be also raised.
In order to overcome the above-noted defect inherent in the prior art, an object of the present invention is to provide a knock detection apparatus for an internal combustion engine in which a threshold value of the knock detection is adjusted by itself so that even if ionic current generation amount is changed due to the change of the fuel or the kinds of the plugs, it is possible to obtain a knock pulse S/N in accordance with a knock/non-knock.
In order to achieve the above object, according to one aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine for detecting a knock generated in an internal combustion engine, in which a vibratory component superimposed on an ionic current generated by combustion of fuel is extracted and shaped in waveform into a pulse waveform by comparison with a threshold value, the number of the pulses in the pulse waveform is calculated by a calculation means, and a control of an ignition timing is performed on the basis of an output result of the calculation means, comprises an integration circuit for integrating (charging) the vibratory component superimposed on the ionic current; and a discharge circuit for discharging a predetermined amount of charge from the integrated charge, wherein the threshold value is self-adjusted by a balance of charge/discharge between the integration circuit and the discharge circuit.
According to another aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the integration circuit integrates (charges) the vibratory component during a predetermined integration period.
According to still another aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the integration period is a fixed time period from a time at which the ionic current that is equal to or more than a predetermined amount is generated during a predetermined period of time.
According to a further aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the integration period is a fixed time period from a time when an integration (charge) voltage is equal to or more than a predetermined value while the integration (charge) of the ionic current starts from the time when the ionic current that is equal to or more than the predetermined amount occurs for a predetermined period of time.
According to a still further aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the integration period is a time period from a time when an integration (charge) voltage is equal to or more than a predetermined value while the integration (charge) of the ionic current starts from the time when the ionic current that is equal to or more than the predetermined amount occurs for a predetermined period of time until the ionic current is equal to or less than a predetermined amount.
According to another aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the discharge circuit performs the discharge at a constant current during a predetermined discharge period.
According to still another aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the discharge period is a fixed time period from a time when the ionic current that is equal to or more than a predetermined amount occurs.
According to a further aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the discharge period is a fixed time period from a time when the ionic current that is equal to or more than a predetermined amount occurs for a predetermined period of time.
According to a still further aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the discharge period is a fixed time period from a time when an integration (charge) voltage is equal to or more than a predetermined value while the integration (charge) of the ionic current starts from the time when the ionic current that is equal to or more than the predetermined amount occurs for a predetermined period of time.
According to another aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the discharge period is a time period from a time when the ionic current that is equal to or more than a predetermined value occurs for a predetermined period of time while the integration (charge) of the ionic current starts from the time when the ionic current that is equal to or more than the predetermined amount occurs until the integration (charge) voltage is equal to or more than a predetermined amount.
According to still another aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the discharge period is a period from a time when the ionic current that is equal to or more than a predetermined value occurs for a predetermined period of time while the integration (charge) of the ionic current starts from the time when the ionic current that is equal to or more than the predetermined amount occurs until the integration (charge) voltage is equal to or more than a predetermined amount and a fixed period following the period.
According to a further aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the vibratory component is shaped in waveform by a second threshold value obtained by adding a predetermined voltage to a first threshold value that is the threshold value.
According to a still further aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the voltage added to the first threshold value is a function of the first threshold value.
According to another aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein an area, to be integrated (charged), of the vibratory component on the basis of at least one of the first threshold value and the second threshold value is only a predetermined portion.
According to still another aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the integration circuit does not integrate (charge) the vibratory component that is not greater than the first threshold value.
According to a further aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the integration circuit does not integrate (charge) the vibratory component that is greater than the second threshold value.
According to a still further aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the integration circuit does not integrate (charge) the vibratory component for a period exceeding the second threshold value.
According to another aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the integration circuit does not integrate (charge) the vibratory component that is not greater than the first threshold value and the integration circuit does not integrate (charge) the vibratory component that is greater than the second threshold value.
According to still another aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the integration circuit does not integrate (charge) the vibratory component that is not greater than the first threshold value and the integration circuit does not integrate (charge) the vibratory component for a period exceeding the second threshold value.
According to a further aspect of the present invention, there is provided a knock detection apparatus for an internal combustion engine, wherein the integration circuit integrates (charges) the vibratory component for a predetermined integration period, and the predetermined integration period is a period starting from a time when the integration (charge) of the ionic current at a time when the ionic current that is equal to or more than a predetermined value is generated for a predetermined period of time while the integration (charge) voltage is equal to or more than a predetermined value until the ionic current is equal to or less than a predetermined amount, the discharge circuit performs discharge at a constant current during a predetermined discharge period, and the predetermined discharge period is a time period from a time when the ionic current that is equal to or more than a predetermined amount occurs for a predetermined period of time is generated while the integration (charge) of the ionic current from this time is started until a time when the integration (charge) voltage is equal to or more than a predetermined level, and a fixed time period following this time, the vibratory component is shaped in waveform by a second threshold value obtained by adding a predetermined voltage to a first threshold value that is the above-described threshold value, the integration circuit does not integrate (charge) the vibratory component that is not greater than the first threshold value and the integration circuit does not integrate (charge) the vibratory component for a period exceeding the second threshold value, and the second threshold value has an upper limit and a lower limit.